Iguanian lizards (Acrodonta and Pleurodonta) from the earliest Eocene (MP 7) of Dormaal, Belgium: the first stages of these iconic reptiles in Europe

We here report on iguanians (both new and the previous record) from the earliest Eocene (MP 7) of the Dormaal locality in Belgium, from the time of the warmest global climates of the past 66 million years. Today iguanians are distributed mainly in the New World (Pleurodonta) and Old World (Acrodonta), having complicated biogeographic histories. Both lineages co-existed in Dormaal 56 Ma. Iguanians here document the presence of thermophilic faunas during greenhouse conditions in the northern mid-latitudes (above 50 degrees north, the latitude of southern England). The complete maxilla of the agamid Tinosaurus europeocaenus is described and figured for the first time, being distinctive and furnishing a number of diagnostic characters. The dentary coronoid process of this species is also observed for the first time. Our morphological analysis supports the previous observation that Tinosaurus is similar to Leiolepis, but also differs from it by several distinguishing features. Some jaw character states present in T. europeocaenus are shared with the Indian T. indicus, Chinese T. doumuensis, and American Tinosaurus sp., but several differences among them are observed. Besides the well-known Geiseltaliellus, we here erect and describe a new pleurodontan taxon. The new taxon is represented by a maxilla with a unique and peculiar tooth crown morphology: the central cusp is bifurcated, markedly split into two distinct and well-separated prongs. This morphology likely indicates a high specialization on feeding sources. This might cause a higher extinction risk relative to generalists, because terrestrial ecosystems in Europe changed substantially during the Paleogene.

Automated summary

This study reports on iguanians from the Dormaal locality in Belgium during the warmest global climates of the past 66 million years. The findings document the presence of thermophilic faunas in the northern mid-latitudes, indicating the existence of greenhouse conditions in Europe. A new pleurodontan taxon with a unique tooth crown morphology was also discovered, suggesting a specialized feeding behavior.